Experimental Flavor Physics
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Search for lepton-flavor violating B -> tau l decays

The baryon asymmetry in the universe tell us that there has to be physics beyond the standard model, so called new physics. An observation of the charged-lepton-flavor violating decay B -> tau l would be a clear evidence for new physics. The reconstruction of this decay is challenging because the two or three neutrinos from the tau decay are not detected. Nevertheless, the B -> tau l decay can be searched for by fully reconstructing the second B meson in e+e- -> Y(4S) -> BBbar events. With the improved algorithm for the full reconstruction of B mesons at Belle II and the conversion of Belle data into the Belle II format one can perform this search with a sensitivity not available before.

Search for new physics in B -> D(*) tau nu decays

The decays B -> D(*) tau nu are one of the few cases where a significant deviation from the standard model was observed in the experiment, namely by BaBar. The recent Belle result is consistent with the BaBar measurement. Therefore it is essential to study these decays in as much detail as possible. With the conversion of Belle to Belle II data, the improved analysis tools for Belle II can be exploited for an analysis of Belle data. This will open new analysis techniques, in particular for the huge dataset at Belle II.

Search for rare decay B -> K(*) nu nu

The LHCb experiment has seen anomalies in the B -> K(*) l+ l- decays. To understand whether this could be due to new physics one would like to compare it to the B -> K(*) nu nu decay. In addition, this decay could be affected by new physics to which B -> K(*) l+ l- is not sensitive. The only experiment where the rare decay involving two neutrinos could be observed is Belle II. To achieve the best sensitivity the analysis technique has to be optimized, which can be exercised on real data before the start of the Belle II data taking thanks to the conversion from Belle data to the Belle II format.

Measurement of time-dependent CP asymmetries in B -> phi K* decays

The indirect CP violation in b -> c cbar s transitions has been measured precisely by the B factory experiments BaBar and Belle and agrees with the standard model prediction. However, in b -> q qbar s transitions, with q = u, d, or s, there is still room for sizable new physics contributions. Using B -> phi K* as a benchmark mode, the techniques for a time-dependent analysis should be established at Belle II and improved compared to Belle where possible.